Any registered user with greater than 30 posts can upload their personal avatar (picture, as you called it). This is accomplished in the User CP section.
The best if you could get your picture in gif why this because the size are small and easy for you to upload. One question your image size is it 60 X 60 ? Do post back.
10k?! That is way too big...
My avatar is a JPEG, but it's size is 3796 bytes, not 10,000...
Make sire the size is smaller than 60x60, and it may not hurt to put the number of colors at 16 instead of 256...
Ive tried around 70 x 85 for my case and the Forum still doesnt want to get the avatar attached. The only way you can make it to attach decrease the size to a lil bit smaller 60 x 65 for instance.
See where it says "Use custom avatar" on the left?
There's a lone radio button that says 'yes' next to it.
Be sure to select it before hitting Submit Modifications.